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United States Patent | 5,020,044 |
Shimonou | May 28, 1991 |
An optical disk system comprising a head positioning system for positioning a head at a desired one of the tracks of an optical disk, and a tracking servo system for maintaining the head at the track by detecting a tracking error signal indicating deflection of the head from the track. In order to accurately position the head to the desired track, a track crossing signal deriving circuit derives an alternating signal component having a frequency corresponding to track crossing of the head from the tracking error signal as a track crossing signal. The track crossing signal is converted to a pulse signal which is counted to produce a counted number as a track crossing number. The track crossing number is compared with a desired track number previously set and a position error signal is produced. A head driving motor is driven until the position error signal becomes zero so that the head is correctly positioned at the desired track. The track crossing signal is converted into a voltage signal as a velocity signal. A slew rate of the track crossing signal deriving circuit is controlled by the velocity signal so that the track crossing signal is reliably derived even if the track crossing velocity increases.
Inventors: | Shimonou; Shigeru (Tokyo, JP) |
Assignee: | NEC Corporation (JP) |
Appl. No.: | 300426 |
Filed: | January 23, 1989 |
Jan 21, 1988[JP] | 63-11923 |
Current U.S. Class: | 369/44.28; 369/30.13; 369/30.17; 369/44.25 |
Intern'l Class: | G11B 021/10; G11B 007/00 |
Field of Search: | 369/33,50,54,116,44,45,44.25-44.35,124,32 360/78.04,77.03,77.04 358/907,342 |
4615023 | Sep., 1986 | Inada et al. | 369/44. |
4719610 | Jan., 1988 | Bates et al. | 369/44. |
4788421 | Nov., 1988 | Ogawa et al. | 369/44. |